1. Field of the Invention
The present invention relates to a novel thermal stabilizer for halogen-containing resins, a halogen-containing resin composition blended with the thermal stabilizer, and a halogen-containing resin-molded article produced by molding the resin composition. More specifically, the invention relates to a compound of the dolomite-type, which is surface treated with a specific compound, a novel thermal stabilizer for halogen-containing resins, which contains the compound of the dolomite-series and the zinc salt of an organic acid, and a halogen-containing resin-molded article produced by molding such a resin composition.
2. Description of the Background
Halogen-containing resins such as vinyl chloride resin are highly flame retardant and have excellent properties including light resistance, recycling potency and chemical resistance. Therefore, the resins are widely used in building materials, pipes, cable coating materials, various sheets, various films and containers.
During molding with the application of heat, the quality of these halogen-containing resins deteriorates. For example, thermal coloring of the resin occurs and the physical properties of the resin such as strength deteriorate because of thermal decomposition of the resin which is accompanied by dehydrohalogenation. In order to overcome such problems, generally, stabilizers are incorporated into halogen-containing resins in order to improve the thermal stability of resins. Suitable such stabilizers (referred to as "thermal stabilizers" hereinbelow) conventionally include metal salts of organic acids such as fatty acids, aromatic carboxylic acids and amino acids. More specifically, lead salts and cadmium salts thereof have been widely used because of their satisfactory property as a thermal stabilizer. Very large amounts of lead-series stabilizers have been used. Because of the seriousness of the toxic problems encountered by using lead salts, their use has been limited. Attention is now focused on organic acid salts of zinc as a safe, alternative thermal stabilizer to the lead stabilizers. However, the thermal stabilization effect of zinc based thermal stabilizer is not satisfactory in comparison to lead based stabilizers. A need, therefore, continues to exist for a zinc based thermal stabilizer for halogen containing resins which exhibits high safety and at the same time exhibits good thermal stabilizing properties.